It is known that the temperature reached in a resistor by its resistive components is currently generally detected by thermostats arranged proximate to, or in contact with one or more of the resistive components.
The temperature of the resistive components of a resistor in fact tends to rise when the components are crossed by a preset current, regardless of whether the resistive components through which the current flows are series- or parallel-connected and are cooled with natural or forced ventilation.
The use of thermostats arranged in contact with or proximate to, one or more of the resistive components entails the fact that the temperature that is detected can be influenced by many external factors and accordingly does not correspond to the temperature actually reached by the resistive components, consequently leading to their failure.
If a thermostat is directly associated with one or more of the resistive components, the technical operating characteristics of the components might in fact be modified, since their structure and configuration are altered.
If instead a thermostat is simply arranged proximate to one or more of the relative components, it does not detect the exact temperature reached by the resistive components, also due to an offset between the time when the resistive components reach the preset temperature and the time when this temperature is reported.
In this case, the delay in reporting that the temperature has been reached may allow the resistive components to reach a higher temperature, which can be fatal to their structure, causing them to burn out and accordingly fail.
U.S. Pat. No. 5,208,741 discloses a chopper circuit utilizing such resistive components and reference may be made to U.S. Pat. No. 4,035,692 for another earlier resistor protection system for use in locomotives.